This disclosure relates to an image forming apparatus provided with a fixing unit, and more specifically to a technology of, in a fixing unit having a mechanism capable of selectively executing driving of a roller or operation of varying fixing nip pressure by switching a rotation direction of one driving input gear, suppressing dislocation of the fixing unit attached to a main body of the image forming apparatus from its attachment position which dislocation is likely to occur at time of the switching of the rotation direction of the driving input gear.
In recent years, in an image forming apparatus of an electrophotographic type or an electrostatic recording type, a fixing unit is typically inserted into a storage part of a main body of the image forming apparatus.
The fixing unit unitizes a large portion of a fixing-related mechanism, and sandwiches, between two rollers of a heat roller and a pressure roller paper on which a toner image has been formed in a former process, then pass the paper therebetween (hereinafter referred to as “a fixing nip part”), thereby being able to heat and pressurize the paper to fix the toner image.
In the image forming apparatus described above, if an image is formed on paper, such as an envelope or thin paper, which is relatively not durable (thin paper), a contact-pressure force (hereinafter referred as “fixing nip pressure” between the two rollers of the fixing unit is too strong, causing a wrinkle in some cases.
Suggested is a fixing device capable of preventing such occurrence of a wrinkle by including applied pressure force adjustment means capable of varying the fixing nip pressure. With this fixing device, in accordance with a kind and a thickness of a recording medium, an applied pressure force and a fixing speed can be set at optimum condition, which can therefore ensure sufficient fixing performance and prevent the occurrence of a wrinkle.